What is being tested?

Inflammation causes red blood cells to stick to each other and form clumps. These clumps are heavier than normal individual red blood cells.

In an ESR, blood is put into a test tube and allowed to settle. If there is inflammation, the red blood cells will clump together and fall quickly to the bottom of the tube. If there is no inflammation, the red blood cells will settle more slowly. Either way, there is a column of clear liquid (plasma, which has no red blood cells) at the top of the tube.

The ESR measures the height of the column of plasma after 1 hour. A low reading means not many cells have settled, which suggests no inflammation. A high reading means a lot of cells have settled, which suggest inflammation.

Why would I need this test?

You might need an ESR test if your doctor suspects that you have an infection or an illness related to inflammation. As ESR is not specific, other tests might be needed to identify the location and cause of the inflammation or infection.

ESR is particularly useful in detecting two specific illnesses: giant cell arteritis and polymyalgia rheumatica.

How to prepare for this test

No preparation is needed for this test.

Understanding your results

A high ESR can indicate inflammation somewhere in the body, but it does not say where or indicate the specific cause.

The ESR also increases with age, pregnancy and in those with anaemia and there are also some blood conditions where the ESR can be lower than normal.

It is important to speak with your doctor about your results.

More information

About ESR testing

See Lab Tests Online for more information about the ESR test.

About blood testing

Visit healthdirect‘s ’Guide to blood testing’ to learn more about blood tests in general with information such as:

• what to consider before having a blood test
• what happens during a blood test
• results accuracy
• blood tests cost.